1. Field of the Invention
The present invention relates to radio frequency IC devices, and particularly to a radio frequency IC device used in a radio frequency identification (RFID) system and a radio communication system including the radio frequency IC device.
2. Description of the Related Art
Conventionally, RFID systems have been developed as article management systems. An RFID system allows non-contact communication between a reader/writer that generates an induction field and an IC chip (also referred to as an IC tag or a radio IC chip) that stores predetermined information and is attached to an article or a container, and thereby allows transmission of information therebetween. The IC chip is capable of communicating with the reader/writer when connected to an antenna, that is, to a radiation plate. A tag antenna disclosed in Japanese Unexamined Patent Application Publication No. 2006-295879 has been conventionally known as one for mounting an IC chip thereon.
This tag antenna has portions of large line width at both ends of a dipole antenna. Mounting an LSI chip on a feeder unit at the center of the dipole antenna allows the tag antenna to function as an RFID system. An inductance unit is disposed around the feeder unit and provides impedance matching between the LSI chip and the dipole antenna.
In the tag antenna described above, only the inductance unit performs impedance matching between the LSI chip and the dipole antenna. This may cause problems in that a frequency range in which impedance matching can be achieved is narrow, an LSI chip having a different impedance cannot be supported, variations in manufacture of inductance units may cause variations in frequency of signals that can be transmitted and received, and thus the tag antenna does not operate as an RFID system.
In the tag antenna disclosed in Japanese Unexamined Patent Application Publication No. 2006-295879, the size of the dipole antenna is reduced by forming, at both ends of the dipole antenna, regions wider than the line width of a dipole portion of the dipole antenna. However, the size reduction of the antenna causes degradation in signal radiation characteristics, and narrows the frequency range in which a desired radiation gain can be achieved.
The present inventors have focused attention on the point that it is necessary for an IC chip of this type to appropriately perform both long-distance communication and short-distance communication. This is because although information is usually exchanged through long-distance communication, specific information may preferably be exchanged only through short-distance communication. For example, in the stage of manufacturing IC chips, when a plurality of IC chips arranged in close proximity are assigned IDs or subjected to characteristic testing, it is necessary that only a specific IC chip be distinguished from adjacent IC chips and allowed to communicate with a reader/writer within a short distance only.
Japanese Unexamined Patent Application Publication No. 2007-79687 discloses a method for testing an RFID tag. The RFID tag includes an antenna that performs communication at UHF-band frequencies and a matching circuit that adjusts impedance of the antenna. For testing the RFID tag, an antenna coil of a reader/writer is placed near the matching circuit of the RFID tag, so that a magnetic flux from the antenna coil causes a control circuit of the RFID tag to operate and thus the RFID tag can be tested.
However, in this RFID tag, the size of the matching circuit is substantially determined by the impedance of an IC. Since it is difficult to increase an area where the magnetic flux crosses, a distance along which the control circuit of the RFID tag can be operated is small.
Japanese Unexamined Patent Application Publication No. 2003-168760 discloses an interposer that firmly electrically connects a substrate having an IC chip mounted thereon to a conductive connecting part of another electrical circuit.